1. Field of the Invention
The present invention relates to a method for imaging and characterizing defects on a semiconductor device which is sensitive to temperature with charged particle beam apparatus, and more particularly, to a method and apparatus for charged particle beam inspection of a semiconductor device with temperature control, and application thereof for characterizing the identified defects by separating, suppressing and/or enhancing specific defect types which are sensitive to temperature in electrical properties.
2. Background of the Related Art
Charged particle beam inspection tools are widely used in the semiconductor industry to examine physical and electrical defects in fabricated devices by observing the difference of grey level profile from the normal devices as a result of charging voltages difference induced by charged particle beam imaging. The image is also known as a voltage contrast (VC) image. For example, a normal feature is expected to be well grounded while an open circuit defect may appear relatively dark in a VC image due to excessive positive charge accumulated (positive charging is induced by scanning the interested device with charged particle beam); this is generally referred to as a dark voltage contrast (DVC) defect. On the other hand, a normal feature is expected to be floating while a short circuit or leakage defect may appear relatively bright due to excessive leakage; this is generally referred to as a bright voltage contrast (BVC) defect.
Different types of defects may appear similar voltage contrast though their generating mechanisms are different. For example, the short circuit defect and the sub-threshold leakage defect may both display as a BVC defect, but the meaning to process control and yield enhancement is totally different.
From the viewpoint of process control and yield enhancement, it is important to identify the defect types because different defects resulted from different root causes and different cures are needed. A short circuit defect is a kind of electrical defect, which is resulted from, for example, a deformed plug contacting its neighboring plug. Also, voids or keyholes formed between contact plugs/vias may lead to a shorted device. This is generally referred to as “piping”. A short defect is fatal to a semiconductor device as it could cause the device inoperable. Leakage is another type of defect with strong dependency on threshold voltage (Vth) of the MOSFET devices. Intrinsic Vth varies with doping density, device dimension, thickness of gate oxide, and environmental factors such as applied voltage and temperature. Whether a leakage defect is fatal to a semiconductor device or not depends on the categories and applications of the devices.
For example, power consumption and performance of ICs are directly related to the leakage current. For low end applications, comparing to dynamic power consumption, the leakage of individual devices which are not actively changing states is often referred to as the static power consumption and is generally negligible to devices when operating. In this case, the leakage defects may be treated as nuisance defects and need to be filtered out of the short-circuit defects and other killer defects.
For high performance IC application, there has been a reduction in the supply voltage (Vdd) with the shrinking device size and thinner gate oxide. While lower Vdd corresponds to lower dynamic power consumption, it also reduces the speed of the device. In order to maintain high performances, efforts have been made to reduce the threshold voltage (Vth) of transistors. However, this encourages occurrence of the sub-threshold leakage and gate leakage. As a result, control of leakage defects in a high-end IC has become critical in current design trends for high speed devices operated at a lower threshold voltage. In particular, the varying sub-threshold voltages of devices over the entire IC being fabricated must be considered, thus there are more and more demand for not only to detect the presence of leakage defects but also to differentiate them from other types of defects, and reveal their severity.
Charged particle beam inspection tool can be used to detect the short/leakage defects as abnormal VCs, but it is often difficult to distinguish between them due to their similar VC images. Also, as mentioned earlier, there are more requirements for inspecting the leakage defect more than just determining its presence, but also for pinpointing the level of leakage.
Accordingly, it is desired to have a method to identify and distinguish between the leakage and short defects on a semiconductor device with charged particle beam apparatus, and to provide more information about the detected leakage defects so they can be characterized or categorized.